FIG. 1 is a working principle diagram of a photoelectric mouse. A ray of light emitted by a light emitting diode 101 is reflected by a working surface 103 after passing through a lens 102. The ray of light containing information about the working surface 103 is subjected to influx by a lens 104 and images in a motion sensing device 105. When the photoelectric mouse moves, its motion trajectory is recorded as a set of high-speed photographed coherent images, wherein each image is referred to as one frame. The motion sensing device 105 calculates the interrelationship among the stored frames in order to recognize the motion of the photoelectric mouse and to output a value of the motion.
FIG. 2 is a method, usually used by the motion sensing device 105 shown in FIG. 1, for calculating motion of a pixel. Starting from a start position, the motion sensing device 105 acquires a first image, referred to as the reference frame. After delaying a predetermined time interval, the motion sensing device 105 then acquires a second image, referred to as the sample frame.
The method illustrated in FIG. 2 generates a predicted motion vector by calculating the correlation between the reference frame and the sample frame in order to obtain moving direction and moving distance of a pixel. When the highest correlation is found by calculating the correlation between the sample frame and the reference frame, if the sample frame moves at least 0.5 pixel to at most 1.5 pixel with respect to the reference frame, the calculating result is moved one pixel. If the sample frame moves more than a predetermined value with respect to the reference frame, the reference frame is updated to the current sample frame, and the updated reference frame is used as the reference frame when the next sample frame is carried out.
In the above method, the movement is recognized in a unit of 0.5 pixel, so the recognition to the movement of the photoelectric mouse can only be updated after the motion sensing device 105 updates the reference frame. Thus, only when the photoelectric mouse moves about 1.0 pixel, the movement of the photoelectric mouse may be recognized. Therefore, the above method cannot recognize the movement of the photoelectric mouse if its movement is less than 1.0 pixel, or a sub-pixel, as a result, resolution is limited.